In recent years, attention has been drawn to automatic dual-clutch transmissions capable of avoiding torque discontinuation at the time of a shift change. As automatic dual-clutch transmissions, there is one which is described in, e.g., JP2007-534899 A (Patent Document 1). The automatic dual-clutch transmission has an output shaft dedicated to a reverse gear, in addition to two input shafts provided coaxially, a first output shaft supporting driven gears at lower-speed stages and a second output shaft supporting driven gears at higher-speed stages. Accordingly, the provision of the output shaft dedicated to the reverse gear gives rise to a problem that the apparatus becomes large in outer diameter as a whole.
On the other hand, German Patent application publication No. 10305241 (Patent Document 2) describes an automatic dual-clutch transmission which does not have an output shaft dedicated to a reverse gear. It is described that the automatic transmission is provided with a reverse gear on a first output shaft supporting forward gears thereon. With this, because an output shaft dedicated to the reverse gear is not provided, it is possible to downsize the apparatus as a whole in outer diameter.